Re: [boost] boost::gregorian::date_period, how to increment/decrement the period

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-03-26 17:59:40

On Sun, 26 Mar 2006 22:25:13 +0000 (UTC), george wrote
> >   template<class point_rep, class duration_rep>
> >   inline
> >   void period<point_rep,duration_rep>::expand(const duration_rep& d)
> >   {
> >     begin_ = begin_ - d;
> >     last_  = last_  + d;
> >   }
> > 
> > Jeff
> 
> thanks Jeff,nice patch.
> but if I want period to get smaller?
> I have to go with a tmp period object?
> are you planing to add a method for this also?
>
> I don't want to play with boost::date_time and do it by myself 
> becouse the source will be open to others and I want to use the 
> 'standard' boost. this patch will be in 1.34?

Well, you could write a 'contract' method.  However, contract is much more
dangerous in that there is the possibility of making an ill formed period. 
I'd stick with the temporary object approach -- you can easily write this into
your own little functions that hide the details.  Something like this:

date_period
contract(const date_period& dp, days len)
{
   if (dp.length() < len) {
     //handle errors here -- after contraction nothing is left...
   }
   return date_period(dp.start() + len, dp.end()-len);  
}

In use:
  date_period dp(....);
  dp = contract(dp, days(2));

expand won't be in 1.34 b/c we've already had a feature freeze.  For now you
could trivially write the expand as I'm suggesting above. 

Jeff